Generally, a wireless communication system is a multiple access system capable of supporting communication with multiple users by sharing available system resources (bandwidth, transmission power, etc.). Multiple access systems include, for example, a code division multiple access (CDMA) system, a frequency division multiple access (FDMA) system, a time division multiple access (TDMA) system, an orthogonal frequency division multiple access (OFDMA) system, a single carrier frequency division multiple access (SC-FDMA) system, and a multi-carrier frequency division multiple access (MC-FDMA) system.
Wireless communication systems have been widely deployed to provide various types of communication services such as voice or data services. Due to dramatic increase in data use as the number of users increases, more frequency bands are required and thus interference problems between adjacent bands have arisen.